1. Field of the Invention
This invention is related generally to apparatus and methods for magnetron sputtering of highly ionized, high-density metal plasmas, and more particularly to magnetron sputtering apparatus that delivers peak powers of 0.1 mega Watts to several mega Watts, with peak power density of 1 kW/cm2 and higher to a sputtering magnetron plasma load with arc handling capability.
2. Brief Description of the Prior Art
It is desirable to coat some substrates by generating metal ions and attracting the ions to the work piece by means of an electrical bias, which attracts the ions. The utility of this approach includes application of coatings to surfaces with irregularities that would prevent uniform deposition by normal sputtering, which essentially requires line of sight. Indeed coating and even filling high aspect ratio trenches in semiconductor devices is possible by biasing the wafer to attract the ions, as reported by Monteiro in JVST B 17(3), 1999 pg. 1094 and Lu and Kushner in JVST A 19(5), 2001 pg. 2652.
A technique for generating highly ionized, high density metal plasma by driving conventional sputtering magnetrons with electrical pulses having high peak power and low duty factor has been reported by Kouznetzov, et al. in Surface and Coatings Technology 122 (1999) pg. 290. Additional teachings can be found by Macak, et al, JVST A 18(4), 2000 pg. 1533; Gudmundsson, et al., APL, Vol. 78, No. 22, May 28, 2001, pg. 3427; and Ehiasarian, et al., Vacuum 65 (2002) p. 147, and U.S. Pat. No. 6,296,742 B1, Oct. 2, 2001.
The appeal of this technique is the ability to generate a large population of ionized species that can in turn be attracted to the work piece by the application of a bias voltage. The above references on the high peak power technique appear to use a simple capacitor discharge through an inductor. However, the technique taught by these references does not disclose any arc handling capability, and in fact suggests that an arc free region actually exists. Unavoidable imperfections in hardware make the physical realization of a completely arc free region of operation essentially impossible, even if its existence is suggested by theory. Use of the technique without arc handling capability makes commercial utilization impractical. Thus, it would be desirable to provide apparatus that enables commercial processes using high peak power pulses to magnetrons to produce high density, highly ionized metal plasmas by minimizing arc energy that in turn keeps product and target damage due to arcing within acceptable limits.
Typically arc control and arc diverting apparatus have been comprised of circuits that either detect the arc and disconnect the power supply from the load or are comprised of a switching circuit that effectively short circuits the power supply to extinguish the arc. These types of arc handling methods are very costly because they may result in a complete shut down of the process wasting expensive stock material, or require dissipation of energy stored in the power supply circuits. In high power applications short circuits to the power supply may result in extremely high currents that can cause destruction of the power supply itself, and repetitive dissipation of stored energy requires expensive resistive elements capable of high peak power and high average power, as well as the means for cooling them.
It would also be desirable if there were provided a magnetron sputtering apparatus and method that could deliver peak powers of 1 mega Watt or greater with arc handling capability for high yield commercial applications. It is an object of this invention to provide a magnetron sputtering plasma system that has the capability to detect arcs and take action to limit the energy delivered to the arc.
There is provided by this invention an apparatus and method for producing a high voltage pulse suited for delivering high peak power to high-density magnetron plasmas with efficient arc handling capability. A pulsing circuit comprised of an energy storage capacitor is repetitively charged and then discharged through an inductor in series with the plasma. The combination of the inductor and capacitor serve to shape the pulse, to provide an impedance match to the plasma, and to limit the current rate of rise and peak magnitude in the event of an arc. An arc is detected by either the fall of the discharge voltage below a preset voltage threshold during a pulse, or an increase in discharge current above a preset current threshold. When an arc is detected the energy storage capacitor is disconnected from the series inductor to stop the current rise. The pulsing circuit is then disconnected from the plasma load and the inductor energy is recycled to the energy storage capacitor.